Organic Superbase as an Efficient Catalyst for Group Transfer Polymerization of Methyl Methacrylate

Organic superbases, 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), proazaphosphatranes (P(RNCH2CH2)3N: R = CH3, TMP; R = i-Bu, TiBP), and phosphazene bases (1-tert-butyl-2,2,4,4,4-pentakis(dimethylamino)-2Λ5,4Λ5-catenadi(phosphazene), t-Bu-P2; 1-tert-butyl-4,4,4-tris(dimethylamino)-2,2-bis[tris(dimethylamino)phosphoranylidenamino]-2Λ5,4Λ5-catenadi(phosphazene), t-Bu-P4) were employed to determine the catalytic activity in the group transfer polymerization (GTP) of methyl methacrylate (MMA). Among the superbases used, TiBP and t-Bu-P4 effectively catalyzed the polymerization to afford poly(methyl methacrylate) (PMMA) with controlled molecular weight and narrow polydispersity. In particular, the molecular weight of the PMMA obtained from the t-Bu-P4-catalyzed GTP was up to 109 600 g mol–1. Only one series of peaks was observed in the MALDI–TOF MS spectra of the PMMAs obtained from the TiBP- and t-Bu-P4-catalyzed GTPs, indicating that both polymerizations proceeded without any side reactions. A postpolymerization experiment further supported the living nature of the TiBP- and t-Bu-P4-catalyzed GTPs of MMA. Furthermore, a mechanistic study of the TiBP- and t-Bu-P4-catalyzed GTPs of MMA was attempted by determining the stereoregularity of the obtained PMMAs and obtaining a series of NMR spectra for the equimolar mixtures of MTS and TiBP or t-Bu-P4.